EP1707026B1 - Method for allocating communication resources and radiocommunication system therefor - Google Patents

Description

The present invention relates to the allocation of communication resources in a heterogeneous radiocommunication system. It relates more particularly to the allocation of communication resources of a subsystem among several subsystems included in the radiocommunication system, the subsystems having different radio access techniques.

It is known that the performance of radiocommunications is largely related to the radio access technique used. By way of example, mention may be made of the Time Division Multiple Access (TDMA) technique, in which the communication resources correspond to distinct time slots on channels having a given frequency. It is also possible to mention the Code Division Multiple Access (CDMA) technique in which the data to be transmitted are modulated by quasi-orthogonal codes known to the transmitter as well as to the receiver.

When a radio system comprises different subsystems using different radio access techniques, the question of traffic distribution may arise. It is indeed desirable to distribute the traffic between the subsystems, according to the performance offered by these different subsystems, so as to obtain the best possible performance. It is further desirable to distribute the traffic between the subsystems so that maximum traffic can flow through the entire system.

This case may occur in particular in the context of a mixed radiocommunication network comprising a second generation subsystem (2G or 2.5G), such as the GSM system ("Global System for Mobile Communication") possibly extended to the GPRS packet data standard ("General Packet Radio Service"), and a third-generation (3G) subsystem, such as UMTS ("Universal Mobile Telecommunications System ") A two-mode radio terminal with communication capabilities in 2G and 3G can then be directed to one of the two subsystems preferentially, so as to optimize the quality of its communications.

First of all, it should be noted that the distribution of traffic in such a mixed system is neither easy nor clearly conceivable by a person skilled in the art because the mobile terminals are attached to one of the subsystems the period preceding their entry into communication. In fact, the communications are thus naturally established on the subsystem of attachment, and it is not obvious to modify such an attachment, which is generally at the initiative of the only mobile terminals, at least in certain systems able to put implementation of data transmissions.

Considering that such an obstacle is removed, a widespread idea is to perform a distribution of traffic in such a system, depending on the type of communications to implement. For example, voice communications are often assigned to the 2G subsystem primarily, while packet data transmissions are typically assigned to the 3G subsystem in priority. A fallback to the other subsystem is only expected when the priority subsystem is saturated. This distribution is based in particular on the idea that each subsystem would be better adapted to the implementation of a given service.

However, it has been found that such a distribution is suboptimal because it neglects the real performance of the subsystems because of their different radio access techniques and / or the spectrum they have respectively. For example, a 2G or 2.5G subsystem typically has a more abundant spectrum (up to 75 MHz in the 1800 MHz frequency band) than a 3G subsystem (whose spectrum can typically have width below 15 MHz, in European 3G networks). For these reasons, a systematic assignment of packet mode communications to the 3G subsystem is highly questionable.

In addition, if the communications of a given first type are largely preponderant compared to the communications of a second type, this mechanism does not solve the problem of allocating new communications of the first type when the subsystem to which they are usually oriented is saturated.

In addition, although it may be possible to calculate by calculation a performance-based allocation strategy for subsystems in extreme traffic scenarios, for example when traffic is almost non-existent or, on the contrary, intense, It is more difficult to define an allocation strategy in average traffic assumptions, which is the most common case in reality. The patent application DE 102 14 934 A1 discloses a radio resource management method in a communication system specifically adapted to carry out handover in a subscriber system provided with several different radio communication subsystems, such as the GSM and UMTS systems. According to this method, decentralized resource management functions provide load measurements on their respective subsystems to a centralized radio resource management function. The latter returns to them load objectives determined dynamically according to the measurements received. This method aims at balancing the respective charges of the communication subsystems.

An object of the present invention is to overcome the disadvantages of the state of the art, by proposing an allocation mechanism taking into account the performance of the subsystems composing the radio system considered.

Another object of the invention is to propose an allocation mechanism intended to allow the flow of a large amount of traffic in the system.

Another object of the invention is to allocate the communication resources of the system with greater flexibility, that is to say without being too dependent on the subsystem of attachment.

Another object of the invention is to define a strategy for allocating the communication resources of the various subsystems of the radiocommunication system, this strategy being applicable to a realistic traffic model, without being limited to extreme traffic hypotheses. .

The invention thus proposes a method for allocating communication resources in a radiocommunication system according to independent claim 1 and a radiocommunication system according to the Independent claim 13. Dependent claims 2-12 provide embodiments of the invention.

The allocation of the resources of the radiocommunication system is therefore performed by considering an indication relating to an occupation of the communication resources, that is to say the load of at least some of the subsystems. This makes it possible not to overload some subsystems with respect to others. This also advantageously makes it possible to optimize the quality of the communications implemented by orienting them towards the subsystem of the radiocommunication system which offers the best quality under the observed load conditions, due to the type of its radio access. For example, a subsystem having a TDMA type radio access will be privileged over a subsystem having a CDMA type radio access, to serve a new communication, when the estimated load on this TDMA subsystem is below a threshold.

The call establishment which requires communication resources on a subsystem of the radiocommunication system means either the start of a new call or the callback on a subsystem of a call that has already started on another sub-system. system eventually.

When the radio terminal for which communication is to be established is attached to a first subsystem, and the resource allocation according to the invention provides support for communication by a second subsystem, the radio terminal is advantageously directed towards the second subsystem prior to the establishment of the communication. This orientation can be controlled at the mobile terminal or result from a distributed parameterization favoring the selection of base stations of the second subsystem.

The allocation of resources may also take into account the type of communications to be established. For example, a packet mode communication will be allocated based on load considerations, such as mentioned above, while a circuit mode communication is preferably carried by the subsystem of the radio terminal concerned.

The allocation of resources may further take into account the quality of service associated with the communications for which resources have been previously allocated. It can also take into account the service implemented for the communication which has to be established, according to the capacities of the different subsystems.

The load to be considered, that is to say the determined indication relating to the occupation of the communication resources, may be the load of the connecting subsystem and / or that of another subsystem. It may also be a global load on a sub-part of the subsystem or a load relating to only a part of the traffic on that subsystem, for example the load for a given mode of communication. only. The allocation is advantageously determined by the subsystem of attachment, from its own load that it evaluates and the load of other subsystems whose estimates are advantageously retransmitted.

The invention furthermore proposes a radio communication system comprising a plurality of subsystems, at least some of the subsystems of the plurality having different radio access techniques to one another, the radiocommunication system being arranged for the implementation of the aforementioned process.

• la figure 1 est un schéma d'architecture simplifiée d'un système de radiocommunication hétérogène dans lequel l'invention peut être mise en oeuvre ; et
• la figure 2 est un organigramme montrant des étapes de procédé selon un mode de réalisation de l'invention.

Other features and advantages of the present invention will become apparent in the following description of nonlimiting exemplary embodiments, with reference to the appended drawings, in which:

• the figure 1 is a simplified architecture diagram of a heterogeneous radiocommunication system in which the invention can be implemented; and
• the figure 2 is a flowchart showing process steps according to one embodiment of the invention.

The figure 1 represents a heterogeneous telecommunication system comprising a 2.5G radiocommunication subsystem and a 3G radiocommunication subsystem. In the following description, we consider such a system with only two subsystems, although the invention also applies to the case where the radiocommunication system comprises more than two subsystems.

The second generation subsystem 1 includes base stations 10 or BTS ("Base Transceiver Stations"), connected to base station controllers 11 or BSCs ("Base Station Controllers"), themselves connected to a switch core network 12 which can be a MSC ("Mobile Switching Center") if one is in a context of communication in circuit mode, or a SGSN ("Serving GPRS Support Node") if one is in a context of communication mode packets.

The third generation subsystem 2 includes, for its part, Node B 20, acting in particular as base stations, connected to radio network controllers 21 or RNC ("Radio Network Controller"), themselves connected to a core network switch 22 which may be an MSC or an SGSN.

The core network switches 12 and 22 are connected, possibly via other switches, to a platform 4, which can be a GMSC ("Gateway Mobile Switching Center") or a GGSN ("Gateway GPRS Support Node") depending on whether the core network switches in question are MSCs or SGSNs. Such a platform allows the interconnection of the heterogeneous radiocommunication system with an external network 5, which may be the Public Switched Telephone Network (PSTN) if it is in a circuit mode communication context, or a network of data transmission by packets or PDNs (Packet Data Network), such as the Internet network.

Radio terminals 3 or UE ("User Equipments") are able to communicate with a remote entity, for example another terminal, via the radiocommunication system. Such communication may be carried out either on subsystem 1 or subsystem 2. Each of the two subsystems of the radiocommunication system represented has a different radio access technique. Thus, the subsystem 1, which is based on the GSM / GPRS communication system, uses the TDMA access technique mentioned in the introduction. As for the subsystem 2, which is based on the UMTS communication system, it uses the CDMA access technique mentioned in the introduction. According to a remark made in the introduction, the frequency spectrum allocated to the subsystem 2 is typically less wide than that of the subsystem 1. However, in another case, the spectrum associated with the subsystem 2 could be identical, even wider than the spectrum associated with subsystem 1.

The UEs 3 support both radio access techniques, so that they are able to exchange information with either of the two subsystems 1 and 2 according to the corresponding radio access technique. If the communication of an UE 3 takes place in connection with one of the two subsystems 1 and 2, it can nevertheless continue on the other subsystem as will be detailed later.

When a UE 3 is not in communication, it can be either in a mode where it is completely "cut" from the radiocommunication system, that is to say that no exchange of information or signaling takes place between the UE and the system (idle mode or "idle" in GPRS), either in an intermediate mode where the UE receives signals from the radiocommunication system, makes measurements, selects a cell covered by a BTS 10 or a Node B 20 and performs updates in collaboration with the network (idle mode or "idle" in GSM and UMTS, or "ready" mode in GPRS). When the UE is in the latter mode, which is generally the case before a communication involving this UE is established, it will be said later, that it is attached to the subsystem 1 when the last cell selected by this UE, possibly following a re-selection of cell, corresponds to a cell covered by a BTS 10 of the subsystem 1, and is attached to the subsystem 2 when the last cell selected by this UE corresponds to a cell covered by a Node B 20 of the subsystem 2. The UE is also capable when it is attached to one of the two subsystems to re-select a cell of the other subsystem as this will be detailed later.

When communication has to be established for a called or calling UE, communication resources, for example one or more time slots in subsystem 1 or one or more codes in subsystem 2, are traditionally allocated to carry this. communication in the subsystem to which the UE is attached, in particular in the radio part of the subsystem concerned. Thus, radio resources are allocated at the base station level covering the cell that was last re-selected by the EU.

According to the invention, the resources allocated to carry such a communication depend on the resource occupancy in the subsystems, that is to say the load values calculated in the radiocommunication system.

An exemplary embodiment of the invention is illustrated on the figure 2 . In step 30, a call is detected, which means that a communication must be established for a given UE 3, in collaboration with the radio communication system of the figure 1 . Such communication may result from an incoming or outgoing call involving the EU 3. It may also result from the resumption of an existing communication on new communication resources, in particular during a mobility of the UE 3 between two coverage areas. In this case, the establishment of the communication corresponds to a transfer of the communication on new resources, according to a procedure of handover or re-selection of cell. The establishment of a communication is thus to be interpreted, in the context of the invention, as the start of a communication or the resumption of this communication on new communication resources.

If the UE 3 considered and the radiocommunication system have both circuit mode (CS) and packet mode (PS) communication capabilities, a first analysis is made after detection of step 30 in the embodiment illustrated in FIG. figure 2 . It should be noted that such a distinction is optional and that it is also possible to allocate communication resources of the radiocommunication system according to the same method, whatever the mode of transmission.

According to a first branch of the alternative, the detected call is in CS mode. At this stage, the UE 3 is attached to one of the two subsystems, according to the last cell that it has selected according to a conventional cell re-selection procedure mentioned above. According to the embodiment illustrated on the figure 2 the communication is then established on the connecting subsystem of the UE 3 (step 31). If, for example, the last re-selection made by the UE 3 in standby mode was for a BTS 10, it means that communication resources are then allocated on the subsystem 1 to implement the communication in CS mode. In particular, radio resources of the BTS 10 in question are allocated to exchange communication frames with the UE 3. On the other hand, if the last cell that has been re-selected by the EU 3 in the standby mode is covered by a Node B 20, the communication is then established on communication resources of the subsystem 2. In particular, radio resources of the Node B 20 in question are allocated to exchange communication frames with the EU 3.

As in the conventional case, communication transfer mechanisms established in step 31 are available. These handover mechanisms, can lead the communication to be transferred to new communication resources within the same subsystem (the radio frames are then exchanged with a new BTS 10 or a new Node B 20), or on resources of the other subsystem than the one on which the communication started at step 31 (inter-system handover). These state-of-the-art mechanisms are largely based on radio condition measurements from the server base station and neighboring base stations, as well as on detection by a controlling organ controlling the base station. waitress, typically BSC 11 or RNC 21, of a transfer condition (degradation of the quality of the current radio link, best available cell, or other). If such a transfer condition is detected, in step 32, a handover, possibly inter-system, can be controlled (step 33). Otherwise, communication continues normally on the home subsystem.

According to the second branch of the alternative, the call detected in step 30 is a call requiring packet mode operation. It's about typically a data transmission, for example at the initiative of the UE 3 considered. We then search the home subsystem for the UE 3, which depends on the last cell re-selected by this UE. It should be noted that, when the radiocommunication system does not know the subsystem of attachment for the UE 3, it has the possibility of conducting a poll of this UE, for example by paging, so as to discover it. In step 34, it is thus sought to know if the UE 3 is attached to the 3G subsystem (subsystem 2 on the figure 2 ).

If the UE 3 is attached to the 3G subsystem, then the load of the subsystem 1 is checked in step 35 (the subsystem 1 will be designated to simplify by "subsystem 2G" in the continuation of the description, even if it supports the GPRS service, that is to say if it is in fact a 2.5G subsystem). For this purpose, the RNC 21 controlling the Node B 20 covering the cell recently re-selected by the UE 3, continuously stores information relating to the charge of the 2G cells of the subsystem 1. Indeed, when UE performs a handover from subsystem 2 to subsystem 1 (handover 3G-> 2G), in circuit mode, indications of the load relative to the target cell of the handover can be transmitted to the source RNC. This information may for example be part of the information provided under the name "New BSS to Old BSS information" in section 3.2.2.80 of Technical Specification TS 148 008, version 5.10.0, "Mobile Switching Center - Base Station System (MSC -BSS); Interface Layer 3 Specification ", published in September 2003 by ETSI (" European Telecommunications Standards Institute "). Once the information relating to the load of the target 2G cell communicated to the MSC / SGSN 22 of the 3G subsystem, the latter can then retransmit them to the RNC 21, for example in a handover execution command message "HO Command ".

Thus, the RNC 21 which stores this information relating to the load of some neighboring cells of the 2G subsystem can deduce therefrom a local load of the subsystem 2G. It then compares the obtained charge value with a threshold value Lt. This value is advantageously chosen so as to optimize the performance of the radiocommunication system. In this example of embodiment, it is considered that transmissions are of better quality when carried by a subsystem with access technology of TDMA type, as long as this subsystem has not reached a load value Lt. Beyond this value, the transmission will be of better quality if it is carried by a subsystem with a CDMA access technology. The value of Lt will therefore be computed beforehand by simulation, and will then eventually be adjusted based on an analysis of the performance actually obtained on each of the two subsystems.

Thus, when in step 35, the estimated charge 2G is greater than Lt, the communication on the 3G subsystem that has a CDMA type access technology will preferably be carried out. 3G communication resources will therefore be allocated to the communication (step 36). These resources include codes on the radio interface between the UE 3 and the Node B 20 covering the cell recently re-selected.

If, on the other hand, the load 2G estimated at the RNC 21 is less than Lt, then one seeks to establish the PS communication on the subsystem 2G. Since UE 3 is attached to the 3G subsystem, the re-selection of a 2G subsystem cell must be performed prior to establishing communication, to ensure that the resources allocated for this communication are resources. 2G (step 37). Such 3G-> 2G re-selection may be in accordance with the procedure detailed in section 8.3.11 of TS 125331 Version 5.6.0, Universal Mobile Telecommunications System (UMTS), and Radio Resource Control (RRC) protocol. specification ", published in September 2003 by ETSI. After the re-selection of a 2G subsystem cell made by the UE on the 3G subsystem radio access network, 2G resources may be allocated to carry the communication. In particular, radio resources are allocated for data exchanges between the BTS 10 covering the newly selected cell and the UE 3, in the form of time slots (step 38) on one or more carrier frequencies.

Optionally, the estimated charge 2G can also be compared to a second charge threshold, the value of which is chosen so as not to not unnecessarily overload the 2G subsystem. Thus, if the load 2G has reached or exceeded such a critical load threshold, resources of the 3G subsystem will preferably be allocated to carry the new communication, even if, moreover, the load 2G is less than the threshold value Lt. This avoids blocking phenomena on the 2G subsystem, which would limit the overall capacity of the radiocommunication system.

Assuming that the UE 3 considered is not attached to the 3G subsystem, it means that it is attached to the subsystem 2G (step 39). As in the previous case, it is then sought to estimate an indication relating to the load on the subsystem 2G, so as to establish communication on the subsystem 2G if its load is below a threshold, or on the sub-system. - 3G system otherwise.

It is thus estimated a 2G load in step 40. This estimate can be made in the 2G subsystem, for example by the use of event counters. These counters can be incremented on the basis of a cell or a group of cells. In order to obtain relevant information on the 2G subsystem load, it will be advantageous to take into account the information counted on a significant number of cells, by adding the counter values obtained for each cell or group of cells.

For this purpose, an estimate of the overall load in 2G is advantageously used, that is to say for all the available communication modes, and in particular both in CS mode and in PS mode, it being understood that an adaptation mechanism may be used in the 2G subsystem to dynamically reserve a proportion of the resources to the CS traffic and the PS traffic according to the respective requests.

The load of the subsystem 2G linked to the traffic CS is deduced for example from a number of requests of a communication resource over a period of observation. As for the load of the subsystem 2G linked to the PS traffic can be deduced for example from the following indicators: the number of contexts of communication (PDP contexts) activated, the number of abnormal losses of data transmissions (the number of losses is substantially related to the number of data transmissions), the load level of the processor of the PCU which is the packet control unit transmitted according to the GPRS service and which can be integrated in a BSC 11 for example (the load of the processor depends on the occupation of the communication resources), the filling of a queue of the PCU containing the units of data to be transmitted (the more the 2G communication resources are requested, the longer the data units remain in the queue ), the bit rate offered in relation to the bit rate required by each user (an offer perfectly meeting the demand is significant of a low occupation of the communication resources), quality indicators on the radio channel such as the RxQual (the quality being all the better that the interference related to the occupation of the radio channels is weak in 2G), the number of blocks and frames transmitted or erroneous, or the ratio, calculated on the u of the PCU, between the number of blocks transmitted on the radio interface and the maximum number of blocks that can be transmitted on all available radio resources for PS traffic (which corresponds to a percentage of radio resource occupancy). Of course, many other indicators than those mentioned above can be used to arrive at a relevant estimate of the load of the 2G subsystem.

In an advantageous embodiment of the invention, the indicators used to estimate the 2G load are weighted according to the quality of service of the users involved in certain communications made in 2G. Thus, if the indicator used is a number of blocks transmitted on the radio interface, the blocks transmitted by a user who subscribed a subscription guaranteeing a very good quality of service are counted with a high multiplier coefficient, while the blocks transmitted by a user who has subscribed without consideration of quality of service are counted with a low multiplier. In this way, the 2G load is artificially over-rated to avoid an influx of new communications to the 2G subsystem, which could bring the quality of service offered below what some users are entitled to expect .

The global load in 2G is then deduced from the load estimates obtained for the traffic CS and PS respectively, for example by summing both estimates. In the case where the estimates are not made by the same equipment, a centralization of the estimates is then made to allow the calculation of the overall load. For example, if the load related to the PS traffic is estimated at a BSC 11, while the load related to the CS traffic is estimated at a PCU, the PCU will then advantageously transmit the result of its estimate to the BSC 11, which will realize the global estimate of the load in 2G. Note that the information relating to the load of the subsystem 2G transmitted to the 3G subsystem in step 35, previously commented, may for example contain the estimate of the load 2G performed in the subsystem 2G, according to the indicators mentioned above.

Once the estimation of the charge 2G is made, it is compared, at the step 40, with a load threshold Lt, which has substantially the same value as the threshold used in the step 35 described above, although a different value can also be considered. When the estimated load 2G is less than Lt, then one chooses to allocate 2G communication resources to carry the new communication (step 42). The BSC 11 which controls the BTS 10 covering the cell which was last re-selected by the UE 3 considered is then advantageously responsible for the comparison of the load 2G with the threshold Lt and the allocation of radio communication resources between BTS 10 and UE 3. Thanks to this mechanism, it is thus ensured that new communications are preferably carried by the 2G subsystem when the radio resources of this subsystem are little occupied.

On the other hand, if the comparison of step 40 indicates that the estimated charge 2G is greater than or equal to the threshold Lt, the allocation of resources of the 3G subsystem is preferred to carry the new communication involving the UE 3 considered. To do this, a 2G-> 3G re-selection is performed. It will be noted that, unlike in the conventional case where the mobile terminal is responsible for autonomously re-selecting cells, the invention provides that the aforementioned re-selection is controlled by the network. This mode of operation controlled by the network is provided in particular by the broadcast or transmission to the UE concerned of the parameter NC2 described in section 10.1.4 of Technical Specification 145 008, version 5.12.0, "Digital cellular telecommunications system ( Phase 2+); Radio subsystem link control ", published by ETSI in August 2003. The 2G subsystem then sends a command to UE 3 to re-select a cell under the control of the 3G subsystem (see section 10.1.4.2). of the aforementioned technical specification 145 008) .This command, called PACKET CELL CHANGE ORDER, as well as the inter-system cell re-selection mechanism are further detailed in the technical specification TS 144 060, version 5.8.0, "Digital cellular telecommunications system (Phase 2+); General Packet Radio Service (GPRS); Mobile Station (MS) - Base Station System (BSS) interface; Radio Link Control / Medium Access Control (RLC / MAC) protocol ", published in September 2003.

Once the 2G-> 3G re-selection has been performed, 3G communication resources are then allocated to carry the communication involving the considered UE 3 (step 44). This allocation controlled by a RNC 21 concerns in particular 3G radio communication resources between the Node B 20 covering the cell that has been the subject of the re-selection 2G-> 3G and the UE 3.

According to an advantageous embodiment, the load of the 3G subsystem can also be estimated before allocating resources to the new communication. This embodiment is the subject of the optional step 41, indicated in broken lines on the figure 2 . It plans to estimate a load on the 3G subsystem and compare it to a threshold value. This avoids passing the new communication on the subsystem 3G, when it has already reached a critical load value Lc, even if the quality of the communication then carried by the subsystem 2G (step 42 ), loaded beyond Lt, thus be suboptimal.

Again, the estimate of the 3G load can be done in a variety of ways. For example, an RNC 21 estimates the occupancy of the 3G radio resources to carry traffic in CS mode. This RNC 21 also evaluates a ratio between a number of data blocks transmitted in PS mode and a theoretical maximum number of blocks that can be transmitted in the same observation period. A summation of the charges related to the CS traffic and the PS traffic can then be performed to obtain an estimate of the overall 3G load. Alternatively, it is sufficient to estimate the 3G load associated with only one of the two modes of communication. For example, the load on PS traffic is only considered if the new communication must itself be performed in PS mode. This avoids switching the new data transmission to the 3G subsystem, when it has its resources reserved for the flow of traffic PS mode already widely occupied. Of course, many other indicators can be used to get an estimate of the 3G load. As additional examples, for the charge related to the PS traffic, the following indicators are cited, which can be consolidated on a 3G cell or on a set of 3G cells (for example all the cells covered by Nodes B under the control of a RNC 21): a number of refused connections between an RNC 21 and a set of UEs, a number of radio access having resulted in a failure, a number of paging requests having resulted in a failure, a charge processor average of an RNC and variations of such a load, a number of codes allocated in relation to the number of available codes, a percentage of the power used compared to a total available power, or other. As in the case 2G described above, the 3G load can be weighted to take into account the quality of service associated with the various users making communications on the 3G subsystem.

Once a 3G load estimate is established, for example for all the cells supervised by an RNC 21, it is advantageously transmitted to the BSC 11 controlling the BTS 10 covering the cell recently re-selected by the UE 3 considered (this transmission can be performed directly if RNC 21 and BSC 11 are interconnected or via other equipment such as MSC / SGSN 12 and 22, or even GMSC / GGSN 4). The BSC 11 in question can thus take into account the 3G subsystem load information in deciding whether to allocate 2G resources to the new communication, or to order the EU to re-selection 2G-> 3G, as in the case described above.

It should be noted that in addition to the load considerations on subsystems 1 and 2, a new PS communication detected in step 30 will also be directed in priority to the 3G subsystem if it corresponds to a service offered only by this subsystem. For example, if the communication requires transfers of a large amount of data in real time (for example for "streaming" applications), it will be served by the 3G subsystem, the subsystem 2G not having sufficient capabilities to support and control such communication. On the other hand, if the communication is carried out according to a service supported by the two subsystems 2G and 3G, for example without any real-time constraint, it will be directed to one of the subsystems according to the method illustrated in FIG. figure 2 . Alternatively, such communication will be carried with a higher priority on the 2G subsystem, so as to leave available resources of the 3G subsystem to future communications requiring a real-time service. The same principle applies depending on the bit rate required for the communication in PS mode detected in step 30: if this bit rate is higher than what the 2G subsystem is able to offer, the communication will be carried by the 3G subsystem, regardless of the respective load of the 2G and 3G subsystems.

In the embodiment of the invention described above, when an inter-system re-selection (steps 37 and 43) is required before the resource allocation of the radiocommunication system, this re-selection is controlled by a controller radio. Thus, if the UE 3 considered is attached to the subsystem 2G, the re-selection 2G-> 3G will be initiated by the BSC 11 controlling the BTS 10 covering the cell recently re-selected by the UE 3. To the Conversely, when the UE 3 is attached to the 3G subsystem, the re-selection 3G-> 2G will be controlled by the RNC 21 controlling the Node B 20 covering the cell recently re-selected by the UE 3.

In another embodiment, inter-system re-selection can be promoted by dynamic parameterization in the core network of the radiocommunication system. Indeed, indicators relating to the load of each subsystem are also available at the level of eg switches MSC / SGSN 12 and 22 and GMSC / GGSN. For example, an SGSN counts the number of PS context contexts (PDP contexts) enabled over an observation period. It is therefore able to deduce an estimate of the occupation of available resources in its coverage area, including radio resources under the control of BSC 11 and RNC 21 connected to it. A finer granularity for the estimation of the load can even be obtained at the level of the core network. In fact, the core network switches are responsible for generating billing tickets for each cell or group of cells. The estimation of the charge can therefore be obtained for such a group of cells.

Moreover, the algorithm of cell re-selection performed by a UE consists in calculating a criterion for a server cell (to which the UE is attached) and a second criterion for neighboring cells, the cell for which the appropriate criterion the largest value being re-selected. The criteria in question include quality radio measurements relating to the cell and neighboring cells respectively. They also take into account parameters broadcast by the network. Among these parameters, the criterion concerning the waiter cell includes a hysteresis aiming at limiting the number of successive re-selections, when the UE is at the border between two or more cells. This hysteresis thus favors the maintenance on the cell waitress. In addition, margins are used in the criterion relating to neighboring cells, to favor or penalize the re-selection of each neighboring cell independently. Finally, a temporal component can also be used in the expression of the criterion relating to neighboring cells in order to avoid too frequent re-selections of cells.

According to this embodiment of the invention, the criteria used in the re-selection algorithm are modified according to the estimated load on at least one of the 2G and 3G subsystems. For example, if we are in step 40 of the figure 2 , and if the load 2G estimated by the MSC / SGSN 12 or the GMSC / GGSN 4 is greater than or equal to the threshold value Lt, then the hysteresis can be reduced for the server cell covered by a BTS 10 to which the UE 3 is attached so as to favor a re-selection, or, preferably, modify the margins applied to the neighboring cells of this server cell, so as to promote the re-selection of cell to a 3G cell covered by a Node B 20, and possibly by penalizing neighboring cells 2G covered by other BTS 10. This increases the probability of the UE 3 performing a re-selection 2G-> 3G, corresponding to step 43 of the diagram of the figure 2 .

Such a modification of the parameters, cell by cell, is advantageously carried out at the level of the operations and maintenance center (OMC), preferably unified for the 2G and 3G subsystems, supervising the system of operations. radiocommunication. It can be carried out manually by an operator, when the latter becomes aware of the load estimates made in the core network, or according to an automatic script having as input parameters load estimates. The new values of the parameters are then transmitted on broadcast channels listened to by all the UEs, so that the latter take them into account.

This method thus makes it possible to promote inter-system re-selections when the load situation of the 2G and 3G subsystems justifies it, or on the contrary to avoid them in the opposite case. It also has the advantage of allowing the UEs to implement the conventional cell re-selection algorithm autonomously, without the need for additional processing and signaling messages resulting therefrom from the radio equipment. radiocommunication system.

In the embodiment of the invention described so far, and illustrated on the figure 2 it was hypothesised, based on the finding mentioned in the introduction, that new communications should preferably be directed to a 2G subsystem with a TDMA radio access technique as long as it was not loaded beyond a certain threshold value, and to a 3G subsystem with a CDMA type radio access technique when the 2G subsystem is loaded beyond the threshold value. The threshold value is determined such that the 2G subsystem performs better, in terms of communication quality, below this value, but lower performance than the 3G subsystem above that value. The example described above thus makes it possible to bring the communication preferably by the subsystem that will give it the best possible quality.

However, the present invention is of a more general nature since it is intended to direct traffic to a given subsystem of a radiocommunication system comprising several subsystems, depending on the load observed on at least some of these subsystems. It therefore also allows a distribution of traffic between subsystems limiting the phenomena of blocking and failure, since the traffic can thus be oriented preferably to a low-load subsystem. An improvement in the overall resource utilization of the system therefore results.

It is thus understood that many other combinations that the example illustrated on the figure 2 are possible. By way of example, it can be envisaged that, unlike the example of the figure 2 , the traffic is first oriented preferably towards the subsystem 3G as it is little loaded, then, when the 3G resources are occupied beyond a load threshold, it is preferably oriented to subsystem 2G.

In addition, more than two subsystems may be used according to the present invention, some of these subsystems having different radio access techniques to each other. Various scenarios can then be envisaged, for example by first prioritizing the use of the resources of a first subsystem as long as its load level is limited, then of a second subsystem as long as its load level is limited, and so on to use the resources of the last subsystem. Then, when the latter itself exceeds a load threshold, allocate resources again from the first subsystem, then from the second subsystem, and so on. Advantageously, in the image of the example illustrated on the figure 2 the subsystems will then be ranked in descending order of the communication quality they offer at low load, so as to optimize the quality of the new communications, at least as long as the overall load of the radiocommunication system remains below a certain limit.

Claims (13)

1. A method for allocating communication resources within a radio communication system comprising at least one first (1) and a second (2) subsystems having different radio access techniques and being able to communicate with radio terminals (3), the method comprising the following steps:

   - an indication is determined related to an occupation of communication resources for at least one of said first and second subsystems;

   - when a communication must be established for a radio terminal, at least one communication resource is allocated from the first or second subsystem in order to carry the communication, taking into account the determined indication.

   Wherein the allocation of at least one communication resource from the first (1) or the second (2) subsystem for carrying the communication relates to at least one communication resource of the first subsystem (1) if the indication related to the occupation of the communication resources of the first subsystem reveals an occupation below a threshold (Lt), and at least one resource of the second subsystem (2) if said indication reveals an occupation above said threshold,
   the method being characterized in that the threshold (LT) is set such that the first subsystem (1) offers a better quality of communication than the second subsystem (2) when its communication resources are occupied at a level below said threshold, and a quality of communication less than the second subsystem when its communication resources are occupied at a level above said threshold.
2. A method according to claim 1, wherein, when the radio terminal for which a communication must be established is attached to the first subsystem (1) and the acceptance of the determined indication implies the allocation of at least one communication resource from the second subsystem (2) to carry the communication, an indication is first transmitted to the radio terminal so that it attaches to the second subsystem, before allocating the communication resource from the second subsystem.
3. A method according to claim 2, wherein said indication transmitted to the radio terminal is a message ordering it to attach to the second subsystem.
4. A method according to claim 2, wherein the radio terminal is arranged to select a base station (10, 20) of the radio communication system based on measurements made on radio signals received from several base stations of the radio communication system and on selection parameters, and wherein said indication transmitted to the radio terminal is a broadcast update of at least some of the selection parameters, said selection parameters being set to encourage the selection of a base station of the second subsystem (2).
5. A method according to any one of the preceding claims, wherein the communications between the radio terminals (3) and the first (1) or second (2) subsystem are carried out in packet mode or circuit mode, and wherein the allocation of at least one communication resource from the first or second subsystem communication resource from the first or second subsystem to carry the communication is performed while taking into account the determined indication only if said communication is to be carried out in packet mode.
6. A method according to any one of the preceding claims, wherein, when the radio terminal for which a communication is to be established is attached to the first subsystem (1), the allocation of at least one communication resource from the first (1) or second (2) subsystem for carrying the communication relates to at least one communication resource of the second subsystem (2) as well if the indication related to the occupation of the communication resources of the second subsystem reveals an occupation below a second threshold (Lc).
7. A method according to any one of the preceding claims, wherein the radio access technique for either the first (1) or second (2) subsystems is code-division multiplexing (CDMA).
8. A method according to any one of the preceding claims, wherein the radio access technique for either the first (1) or second (2) subsystems is time-division multiplexing (TDMA).
9. A method according to any one of the preceding claims, wherein the second subsystem (2) has a much less broad frequency spectrum than the first subsystem (1).
10. A method according to any one of the preceding claims, wherein the indication related to the occupation of the resources takes into account a quality of service associated with the communications for which the resources were allocated.
11. A method according to any one of the preceding claims, wherein each of the first (1) and second (2) subsystems is arranged to determine the indication relating to the occupation of its own communication resources, and to obtain the determined indication related to the occupation of communication resources of the other subsystem, and wherein whichever of the first and second subsystems the radio terminal is attached to determines whether the communication resource to be allocated to carry the communication is a resource of the first or second subsystem.
12. A method according to any one of the preceding claims, wherein the first subsystem (1) is able to communicate with the radio terminal (3) according to a first set of services and the second subsystem (2) is able to communicate with radio terminals (3) according to a second set of services, and wherein the allocation of at least one communication resource from the first or second subsystem to carry the communication further takes into account the service implemented for said communication.
13. A radio communication system comprising a plurality of subsystems (1, 2), at least some of the subsystems of the plurality having different radio access techniques among them, the radio communication system being arranged to implement the method according to any one of the preceding claims.

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